Rotary wing blade



Sept. 9, 1952 DALAND 2,609,883

ROTARY WING BLADE Filed NOV. 29, 1946 2 SHEETS SHEET l Sept. 9, 1952 E. DALAND ROTARY WING BLADE 2 SHEETS--SHEET 2 Filed Nov. 29, 1946 Patented Sept. 9, 1952 Elliot Daland, Wallingford, Pa.,

assignor, by

mesne assignments, to Piasecki Helicopter Corporation, Morton, Pa.

Application November 29, 1946, Serial No. 713,039

Claims.

This invention relates to improvements in rotary wing aircraft blades used with hubs provided with pitching and flapping axes and to improved methods of manufacturing and balancing the same.

The principal object of this invention is to provide a rotor blade structure wherein the mass distribution is so related to the lift distribution that bending forces acting on the blade will be reduced to a minimum. I

Another object of this invention is to provide a blade structure that will withstand the loads imposed thereon and still be light in weight and easy to manufacture.

A further object of this invention is to provide a blade whose chordwise aerodynamic center of pressure is located aft of the center of gravity of the blade.

A still further object of this invention is to provide an improved method of manufacturing and balancing blades that will assure smoother operating rotors and reduce blade fatigue.

Another object of this invention is to eliminate the use of heavy balancing weights at the leading edge of the blade for the purpose of shifting the center of gravity of the blade forwardly.

Other objects and advantages will become apparent when the following description is read in conjunction with the accompanying drawings.

In the drawings:

Figure 1 represents a plan view of the preferred embodiment of my invention.

Figure 2 is a cross section taken on line 2-2 of Fig. 1.

Figure 3 is a cross section taken on line 3-3 of Fig. 1.

Figure 4 is a cross section taken of Fig. 1.

Figure 5 is a detail cross section taken on line 5-5 of Fig. 1.

Figure 6 is a front elevation view of the blade illustrating the distribution of the lift forces along the span of the blade.

Figure 7 illustrates the chordwise distribution of forces acting on the blade.

The blade is made up to form a symmetrical airfoil when viewed in cross section in the preferred embodiment of this invention. However, other airfoil shapes may be chosen without departing from the scope of this invention. In plan, the blade is of generally rectangular shape.

The center of pressure of the lift of this type blade is located approximately 25% of the chord from the leading edge, and acts upwardly as shown by the arrow L in Figure 7 of the drawings.

on line 4-4 As it is necessary to provide a change of lift of the blades, it is common practice in the helicopter art to mount the blades in pitch bearings usually located near the root end of the blade. The rotative axis of the pitch bearings is parallel to the longitudinal axis of the blade and in the present invention coincides with the axis of the metal spar member.

To stabilize the control system, I have found it desirable to provide a diving moment about the blade pitch axis. This is done by moving the center of gravity of the blade ahead of the center of pressure so that a lift moment arm (ZCL will exist under all conditions of flight.

Heretofore, the chordwise center of gravity of the blades has been brought forward by adding heavy weights along the full length of the leading edge. In the present invention these weights have been eliminated by providing a structure wherein the main structure members are located in the nose section of the blade ahead of the chordwise center of pressure to cause the chordwise center of gravity to be ahead of the center of pressure.

The blade structure is made up of a step tapered tubular metal spar II, wood or plastic members I2 and I3 fitted to the front and rear surfaces of the spar I I and cemented thereto. Secured to the strip I3-a glued to the member I3, are ribs I 4 located at spaced intervals along the length thereof. The ribs I4 extend rearwardly to a trailing edge member I5 to which they are at tached.

The top and bottom of the blade is covered with sheets I6 and I! of plywood or plastic suitably glued and fastened to the members I2, I3, I4 and I5 and are joined together aft of the trailing edge member. To complete the airfoil shape, a nose strip is attached to the front of the member I2 and edges of the covering sheets I6 and I! by glue and screws. For purposes of spanwise weight distribution the nose strip is made up of two or more sections, I8 and I9. The inboard or root end section I8 being lighter material than the outboard or tip end section I9.

Because of the high forces acting on the heavier nose strip located at the outboard portion of the blade, a different fastening means is employed. This means is shown in detail in Figure 4 of the drawlngs wherein it will be noticed that bolt 2| passes thru the members I9, I2, and I3 and II. This bolt is screwed into a nut 22 fastened to the back of the member I3. To strengthen the spar I I at the points where the bolt passes there thru and to provide greater bearing surface for the bolt, lugs 23 are welded to the spar. The lugs 23 project into the recesses formed in the members I2 and 13. This construction not only provides a safe and efiicient method of holding on the nose section but also acts to prevent any relative angular or longitudinal displacement between the blade structure and, the metal spar.

Due to the length and shape of the blade and for manufacturing reasons it has been found desirable to cover the blade with several sheets of covering material suitably joined together.

To assist in forming the joint and to reinforce the same, two of the ribs l4 are located at each side of the joint as shown in Figure5. these ribs and underlying the scarf joint and glued thereto are strips 24. These cap strips act as a backup plate when clamps are applied to form the joint and also act to tie the ends of the plywood or plastic covering together after the joint is formed.

The lift forces acting along the span of the blade are approximately-as show-n in Figure 6 by the vertical arrows. These forces are opposed by centrifugal force acting in an opposite direction due to theconing angle taken by the blade.

To prevent bending moments on the blade it is necessary that the opposing forces be equal in magnitude to the lift forces along the span. To obtain this result the blade must increase in weight as it extends outwardly from theroot to the tip.- This is accomplished by providing-lightening holes 'spaced close together near the root end and gradually being spaced further apart toward the outboard end. Near the tip endwhere the'lift forces are very high weightis added by using a heavier nose strip i9.

Inviewing the blade in plan view as shown in Figure 1, it will be'noticed that the leading edge of theblade is stepped back at approximately the samepoints that spar is tapered down. This is done to keep theweight of the spar close to the leading edge so that the chordwise center of gravity is ahead of the chordwise center of pressure and for fairing reasons.

Forming an important part of this invention is my method of obtaining dynamic balanceof the, blades so that smoother operation and smaller. bending moments in the blades may be expected of a rotor using these blades. This is done by first determining th spanwise liftadistribution and then designing the blades so that thespanwise mass distribution will producecentrifugal forces proportional to the spanwise-lift forces. The chordwise and spanwise weight moments resulting from-the-mass distributionas determined above are computed and these weight. moments are then specified for purposes of static balance. Static balance of the blade'is accomplishedin three operations aboutthe lead,- ingedge of the blade; First, the chordwise about the root end of the blade is determined; Third, Weight is added to or taken from thegspanr wise station near the blade'tip to correct the spanwise balance to the specified'weight moment,

the chordwise location of this. weight adjustment. being located at apoint that will correct, thev chordwise weight moment toward: the. specified chordwise moment.

While the preferred embodiment of the, inven- Bridgingv weight moment of the completed blade is determined. Second, the spanwise weight moment.

I claim:

1. In a lift rotor for a rotary wing aircraft, an elongated blade comprising a series of contiguous spanwise extending sections, the mass distribution of said blade being such that the centrifugal force generated by the mass of any one of said sections provides a force component equaland opposite to the aerodynamic lift generated at said one section when said blade is operated at a predetermined operational speed of rotation and toning angle.

2. In a lift rotor for a rotary Wing aircraft, an elongated blade comprising a series of contiguous spanwise extending sections, a step tapered tube, the inboard end of said tube being of greater diameter than the outboard end, a leading edge, a. trailing.v edge, said, leading edge being step tapered in the same direction and magnitude as the step tapered tube, each step of said leading edge being parallel to the axis of said tube and each succeeding outboard stepbeing progressively closer to-the axis of said tube, saidtrailing edge being parallel toand equidistant from the axis of said tube throughout the span of said blade, the mass distribution of said blade beingsuch that the centrifugal force generated by the mass of any one of said'sections providesa force component equaland opposite to the aerodynamic lift generated at said one section when said blade is operated at a predetermined operational speed of rotation and coning angle.

3; A blade as recited in claim 1 andhavin a leading and trailing edge and comprising a series of contiguous spanwise extending sections, astep tapered: tube, the inboard end of said tube having a greater diameter than the outboard end, a first non-metallic member extending along the span of said tube and bonded to the frontface thereof, a second non-metallic member extending along the span of said tube andbonded'to the rear face thereof, a non-metallic nose strip fixed, to the front face of said first member along the inner portion of said blade, a-metallic nose stripfixed to the front face of the outer portion of said first member, a series of ribs extending rearwardly from said second member and. fixed thereto, a covering fixed to the upper and lower surfaces of said first and second members and said ribs, said covering abutting said nose. strips,

the taper of said tube in such a manner that the leading edge alongthe outer step is paralleli to and closer to the axis of said tube than the lead; ing edge of the next inboard step, the distance between the axis of said tube and the trailing edge being constant throughout the spanof. the

' blade.

4. In alift. rotor for a rotary wing aircraft; an

elongated blade comprising. aseries of contiguous spanwise extending sections, a step taperedtub'er the. inboard end of said tube being-of greater diameter than the outboardlend', aleadin'gedge, a. trailing. edge, said leading edge being step taperedsin thesame direction andmagnitude-as the; step. .taperedtube; eachstep. of said leading.

edge being paralle-ltothe axisof said tube and each succeeding outboard step: being progresf sively closer to the axis of saidtube', said trailing '51 In alift rotor 'for a-rotary wing aircraft, an

elongated blade having a leading and trailing edge and comprising a series of contiguous spanwise extending sections, a step tapered tube, the inboard end of said tube having a greater diameter than the outboard end, a first non-metallic member extending along the span of said tube and bonded to the front face thereof, a second non-metallic member extending along the span of said tube and bonded to the rear face thereof, a non-metallic nose strip fixed to the front face of said first member along the inner portion of said blade, a metallic nose strip fixed to the front face of the outer portion of said first member, a series of ribs extending rearwardly from said second member and fixed thereto, a covering fixed to the upper and lower surfaces of said first and second members and said ribs, said covering abutting said nose strips, the thickness of said blade varying in conformity with the taper of said tube, the leading edge of said blade being step tapered in conformity with the taper of said tube in such a manner that the leading edge along the outer step is parallel to and closer to the axis of said tube than theleading edge of the next inboard step, the distance between the axis of said tube and the trailing edge being constant throughout the span of the blade.

ELLIOT DALAND.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,428,714 Schwamb et al Sept. 12, 1922 2,070,657 Hafner Feb. 16, 1937 2,111,975 Larsen Mar. 22, 1938 2,152,861 Bennett Apr. 14, 1939 2,272,439 Stanley Feb. 10, 1942 2,303,707 Pullin Dec. 1, 1942 2,305,247 Fisher Dec. 15, 1942 2,343,383 Martin et a1 Mar. 7, 1944 2,388,485 Jensen Nov. 6, 1945 2,412,908 Platt Dec. 17, 1946 2,467,031 Hess et a1 Apr. 12, 1949 

